Patent GB-767684-A (GB)
Title: Improvements in and relating to automatic telephone exchanges
IPC: H04Q11/04
Filed: 1952-12-03
Abstract: 767,684. Automatic exchange systems. GENERAL ELECTRIC CO., Ltd., and WARD, P. W. Dec. 3, 1953 [Dec. 3, 1952], No. 30675/52. Class 40 (4). Subscribers' line terminating units and trunk terminating units connected respectively to opposite ends of a multiplex transmission link, may utilize any free carrier to effect a connection through the link. Some at least of the trunk terminating units are connected together in pairs for providing connections between subscribers associated with the same transmission link, two carriers then being utilized, one by the called and the other by the calling subscriber. The carriers may be oscillations of different frequencies in which case the trunks may either be audio links or contain frequencychangers translating from one carrier frequency to another directly; or, as described in detail, the carriers may be time division multiplex pulses. Trunking. A 10,000 line exchange comprises twenty 500 line groups each served by a multiplex switch having 210 outlets. 190 of these are used for 19 groups of ten trunks to the other 500 line groups and the remaining 20 are connected at the ends of 10 trunks for establishing calls within the 500 line group. The multiplex switches themselves are capable of establishing 80 simultaneous speech paths to the outlets, a subscriber's line circuit and a trunk terminating unit being connected by providing associated modulator/demodulator units with a pulse train of the same phase which is not allotted until the connection is to be set up. Pulses used. Fig. 2 illustrates the pulses used and provided by the generator 25 (Fig. 13). The M pulses provided at terminal TM are 0.5 Ásec. pulses having a recurrence period of 1 Ás. These pulses are actually emitted from the generator as a 1 Mc/s. sine wave being adjusted in phase and squared at the equipment using them. The pulses are used to provide 100 multiple channels each with a pulse recurrence frequency of 10 kc/s. The R pulses provided at terminal TR have a positive period of 20 Ás. and a negative period of 80 Ás., the respective periods being used to divide the M pulses into two series, the first 20 being used for providing 20 " service " channels and the last 80 for providing speech channels in the multiplex switches. The M and R pulses are illustrated in Fig. 2 (a). Fig. 2 (b) illustrates three of 25 P pulses and one of 24 Q pulses on a reduced scale. Each of these is of duration 100 Ás., have pulse recurrence frequencies of 2.5 ms. and 2.4 ms. respectively, as shown in Fig. 2 (c). Two of these pulses coincide at 60 ms. intervals and 600 distinct coincidences occur between the various P and Q pulses. 500 of these are used to identify wanted subscribers within their groups of 500. Pulses TC1 ... 5 are the first five M pulses and are used for associating a calling line with one of five registers. TC6 and TC7 are used to control release. General description. Calls between subscribers in different 500 line groups. When a subscriber 10, Fig. 13, lifts his hand-set a relay 28 operates and emits a potential on lead 30 which passes via gate 32 to open gate 35. This gate is provided from the allotter equipment 49 with an M pulse corresponding to a free register and passes it via a combining circuit 38 to a channel pulse generator 40. This generator is fed with all the M pulses and operates as a 100: 1 frequency divider, the phase of the output pulse being that of the pulse received from the circuit 38. This pulse which is here assumed to be TC4, is fed to the modulator/demodulator circuit 27. The pulse TC4 also being fed to the modulator/demodulator 47, the calling subscriber 10 is now connected over the multiplex path 12 to the register 48 which receives the dialled digits. The register has twenty terminals T1 ... T20 each corresponding to a 500-line group which may contain the wanted party. Over the appropriate terminal, e.g. that indicating that the wanted subscriber is in the 500-line group associated with the multiplex switch 239, a pulse is emitted whose position is determined by the coincidence of a P and a Q pulse and identifies the wanted subscriber within the group. A trunk allotter 24<SP>1</SP> is provided for each group of inter-switch trunks and is provided with five input terminals TI1 ... 5 for the registers associated with the multiplex circuit 12 and five terminals TI6 ... 10 for the registers associated with the multiplex circuit 239. The trunk allotter selects a free one from the group of inter-stage trunks, say trunk 21<SP>1</SP>, and injects the incoming pulse into that trunk. The pulse is also emitted on terminal 65<SP>1</SP> (if the allotter had been seized over TI6 ... 10 the pulse would have been emitted on 65<SP>11</SP>) and passed to the gates 67 of the subscriber's line circuits in the wanted group. In the wanted subscriber's line circuit this pulse in combination with appropriate P and Q pulses open the gate 67 to admit from the speech pulse allotter 69 a pulse corresponding to a free speech channel in the multiplex circuit 239. The channel pulse generator 40 is thus set to generate a pulse having the same phase and this is fed to the modulator/demodulator 27. The trunk allotter also emits the pulse over lead 256 to gate 77 of the trunk terminating unit 243 to admit the same free speech channel pulse from the speech pulse allotter 69 to the channel pulse generator 75 which thereupon delivers pulses having this phase to the modulator/demodulator 74. The wanted subscribers 240 is now connected to the trunk 21<SP>1</SP> over one of the channels of the multiplex unit 239. The pulse emitted by the register is also reverted to the modulator/ demodulator 47 which samples it and reverts a pulse over the multiplex path to the calling subscriber's modulator/demodulator which thereupon produces a short pulse which is admitted by the gate 81, opened by an R pulse, to a pulse lengthener 82 which lengthens the pulse to 100 Ás. The lengthened pulse opens the gate 83 to pass a free speech channel pulse from the speech pulse allotter 69 associated with the multiplex 12. This pulse then passes to the channel pulse generator 40 whose phase is thus reset to the phase of the allotted speech pulse. The output from the trunk allotter also opens the gate 77 of the trunk terminating unit 242 to admit the free channel pulse from the allotter to set the channel pulse generator 75 controlling the modulator/demodulator 74. Connection from the calling line to the trunk 21<SP>1</SP> and thence to the called line is thus established. With the calling subscriber's channel pulse generator no longer generating pulse TC4, the register 48 is released. When the speech path is set up the called subscriber's modulator 27 emits a D.C. signal which in combination with D.C. on lead 31 from relay 28 when the receiver is on the hand-set opens a gate 29 which permits the passing of ringing current from a source TRT to the called subscriber. When the called subscriber lifts his hand-set, relay 28 removes D.C. from lead 31 to close the ringing gate 29. When either subscriber hangs up, his relay 28 reapplies D.C. to lead 31, causing the circuit 85 to produce a 100 ms. pulse which is passed to gates 86 and 87. The latter remains closed over the inhibiting lead 84 which is fed with D.C. whilst the demodulator 27 is receiving pulses from the multiplex link, but 86 opens to pass an audio-frequency oscillation TT to the modulator 27. When this is received in the trunk terminating unit 243 (say) it is accepted by a filter 79 to open a gate 78 which admits pulses TC7 to reset the channel pulse generator 75 to a phase corresponding to a permanently idle channel. The modulator/demodulator 27, no longer receiving pulses in phase with those from its channel pulse generator, ceases to emit D.C. on lead 84, thereby permitting the pulse from circuit 85 to open the gate 87 to admit a pulse TC6 to shift the pulse generator 40 to the phase of a second permanently idle channel. Calls between subscribers in the same 500 line group, Fig. 12. In this case two pulse channels have to be seized in the same multiplex circuit, one for connecting a trunk to the calling line and the other for connecting the trunk to the called line. Thus the two connections have to be staggered in time to prevent an attempt to use the same pulse for both connections. The register is therefore caused to emit a second pulse delayed 100 Ás. compared with the pulse normally emitted and a modified form of trunk allotter is used. As shown, Fig. 12, the register emits over lead 52 a pulse whose position indicates the position of the wanted subscriber in his 500 line group. This pulse emerges from the allotter over lead 65 and is fed to all gates 67 of the group in the normal way and the free channel pulse offered by the allotter is used to set up the called subscriber's channel pulse generator 40. The pulse on lead 52 is also emitted over the lead 58<SP>1</SP> to open the gate 77 of the trunk terminating unit 18 so as to admit the pulse offered by the speech pulse allotter to the channel pulse generator 75. With the respective modulator/demodulator units pulsed by the same pulse, the called subscriber's circuit 14 is thus connected to the trunk terminating unit 18. With this pulse now in use a different pulse is offered by the speech allotter. During the next 100 Ás. period a pulse emitted on lead 53 from the register is passed through the allotter 24 to lead 58<SP>2</SP> to open gate 77 of the trunk terminating unit 17 to admit the next pulse offered by the speech pulse allotter 69 to the channel pulse generator 75. The pulse from the register is also routed to the modulator/ demodulator 47 for reversion through the multiplex circuit to the calling subscriber's line circuit to effect the admission of the offered speech pulse to the channel pulse generator 40 as previously described, and the calling subscriber is thus connected to the trunk te